This striking Art Deco-era necklace fuses richly hued onyx with a dazzling array of antique diamonds. Crafted in platinum, the 2.5-inch drop pendant doubles as a brooch - or a chain extender, for those wanting to add a bold focal point to their layers. The angular onyx plaque features subtly faceted edges that catch the light, drawing the eye to the central Old Mine Cut diamond (estimated at 2-2.16ct), flanked above and below by two old cut diamonds (approx. 0.75ct each), showing a mix of Old Mine and early European characteristics. Each is set within intricate platinum milgrain borders.
Whimsical platinum fleur-de-lis motifs adorn the pendant’s sides and compass points, set with a mix of antique cuts, including Old Mine, rose cuts, and single cuts. Four smaller old cut diamonds (approx. 0.15ct each) accent these flourishes - one thoughtfully replaced with a rose cut during a historic repair, adding a layer of charm and authenticity.
Further highlights include two onyx spacer beads and a secondary angular onyx accent, set with a 4mm Old Mine Cut diamond. The necklace is finished with dual bolt ring clasps - one acting as a safety chain while also enabling the chain to be worn at either 16 or 16.75 inches.
In very good antique condition. There is a minor nibble to the onyx on one side of the central diamond setting; however, due to the jet-black colour and the tall profile of the diamond casting a natural shadow, it is not noticeable when worn. Some small nibbles are visible on a few of the smaller diamonds - expected with a piece of this age and use.
With approximately 4.65-5 carats total diamond weight, this heirloom-quality piece is sensational worn as a necklace, as a standalone brooch, or used to extend your favourite chains - as shown in one of our modelled photos.
Art Deco Platinum Onyx & Old Mine Cut Diamond Convertible Necklace
- Era: Art Deco
- Metal: Platinum
- Stones: Natural antique diamonds (approx 4.65-5ct total)
- Dimensions:
- Necklace length: 16-16.75 inches
- Pendant/brooch:
- Length: 38mm
- Width: 22.5mm
- Thickness: 5mm
- Weight: 16.48g including brooch fittings
- Hallmarks: No noticeable hallmarks. Professionally tested on an XRF analyser to confirm the metal purity.
- Condition: Very good antique condition
Unless otherwise stated, any chains, jewellery boxes, and other items photographed with the listed piece are for advertising purposes only and not sold with this piece.






























